Since the enchantment mechanics changed, a hint of the enchantment is shown. According to the wiki it isn't changed until you enchant something, However the hint does change when you close/reopen a singleplayer world.

How to reproduce:
1. Put a tool in the enchantment slot, in the enchantment table UI.
2. See the enchantment hints and levels.
3. Pick it back up (do not enchant it), and immediately exit the world.
4. Reopen the world and put the same tool into the enchantment table again.
EDIT: This was originally discovered on a multiplayer server, and is reproducible via disconnect/reconnect too.

Expected result: The hints and the levels are the same.
Actual result: The hints and levels are different.